The present invention relates to a method of determining the direction of rotation of a member, such as a rotating shaft, and more particularly, to a speed pick-up wheel or rotor which is adapted to be mounted on the rotating shaft.
In a typical system of the type with which the present invention may be utilized, it is the intention to sense both speed of rotation and direction of rotation, of the rotating member. However, a number of generally acceptable methods, devices, and logic circuits are already known for use in determining the speed of rotation, and therefore, the description of the present invention will focus almost entirely on determining the direction of rotation of the rotating member.
As is well known to those skilled in the art, most methods and devices for determining speed and direction of rotation of a member, such as a shaft, involve positioning on the shaft some sort of a pick-up wheel or rotor, which typically is a gear wheel having a plurality of teeth about its outer periphery, circumferentially equally spaced apart.
One known method for sensing direction of rotation involves modifying the profile of the teeth on the rotor in such a way that the resulting signal, as the tooth passes in close proximity to a sensor, has a different shape if the shaft is rotating clockwise than if the shaft is rotating counter-clockwise. For example, it is known to provide teeth on such a rotor having a "saw-tooth" configuration, whereby the amplitude of the resulting signal will increase gradually, then drop sharply in one direction of rotation, but will increase sharply then drop gradually in the other direction of rotation. Although such a tooth configuration conceptually provides an acceptable method of sensing direction of rotation, the necessity of sensing one wave form versus another adds substantially to the complexity of the required logic system, and introduces a substantially greater opportunity for error.
A substantially different approach to sensing direction of rotation is to provide two different sensors, each of which has a sinusoidal signal produced thereon, in response to the rotation of the rotor, with the sensors being positioned to result in phased signals, for example, where one signal leads the other by 90.degree.. Such an approach to detecting direction of rotation is illustrated in U.S. Pat. Nos. 3,728,565; 4,331,917; and 4,370,614. Utilizing such an approach has the advantage of greater accuracy in sensing direction of rotation, but the necessity for two separate sensors, and the additional logic circuitry adds substantially to the complication and expense of both the system hardware and software.